Under physiological conditions, multicomponent biological membranes undergo structural changes which help define how the membrane functions. An understanding of biomembrane structure-function relations can be based on knowledge of the physical and chemical properties of pure phospholipid bilayers. Here, we have investigated phase transitions in dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC) bilayers. We demonstrated the existence of several phase transitions in DPPC and DOPC mica-supported bilayers by both atomic force microscopy imaging and force measurements. Supported DPPC bilayers show a broad L(beta)-L(alpha) transition. In addition to the main transition we observed structural changes both above and below main transition temperature, which include increase in bilayer coverage and changes in bilayer height. Force measurements provide valuable information on bilayer thickness and phase transitions and are in good agreement with atomic force microscopy imaging data. A De Gennes model was used to characterize the repulsive steric forces as the origin of supported bilayer elastic properties. Both electrostatic and steric forces contribute to the repulsive part of the force plot.

We analytically and numerically analyze the fluorescence decay rate of a quantum emitter placed in the vicinity of a spherical metallic particle of mesoscopic size (i.e with dimensions comparable to the emission wavelength). We discuss the efficiency of the radiative decay rate and non-radiative coupling to the particle as well as their distance dependence. The electromagnetic coupling mechanisms between the emitter and the particle are investigated by analyzing the role of the plasmon modes and their nature (dipole, multipole or interface mode). We demonstrate that near-field coupling can be expressed in a simple form verifying the optical theorem for each particle modes.

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The membrane surface of living CV-1 kidney cells in culture was imaged by contact-mode atomic force microscopy using scanning forces in the piconewton range. A simple procedure was developed for imaging of the cell surface with forces as low as 20-50 pN, i.e., two orders of magnitude below those commonly used for cell imaging. Under these conditions, the indentation of the cells by the tip could be reduced to less than l0 nm, even at the cell center, which gave access to the topographic image of the cell surface. This surface appeared heterogeneous with very few villosities and revealed, only in distinct areas, the submembrane cytoskeleton. At intermediate magnifications, corresponding to 20-5 microm scan sizes, the surface topography likely reflected the organization of submembrane and intracellular structures on which the plasma membrane lay. By decreasing the scan size, a lateral resolution better than 20 nm was routinely obtained for the cell surface, and a lateral resolution better than 10 nm was obtained occasionally. The cell surface appeared granular, with packed particles, likely corresponding to proteins or protein-lipid complexes, between approximately 5 and 30 nm xy size.

Spatially resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) has been used to investigate as fluidic phase in nanoubbles embedded in a metallic P d90P t10 matrix. Using the 1s → 2p excitation of the He atoms, maps of the He distribution, in particular of its density an pressure in bubbles of different diameter have been realized, thus providing an indication of the involved bubble formation mechanism. However, the short-range Pauli repulsion mechanism between electrons on neighboring atoms seems insufficient to interpret minute variations of the local local measurements performed at the interface between the metal and the He bubble. Simulations relying on the continuum dielectric model have show that these deviations could be interpreted as an interfzce polarization effect on the He atomic transition, which should be accounted for when measuring the densities within the smaller bubbles.Confined fluids in nanosized volumes constitute challenging objects for both basic and technological aspects. The investigation of the structural features and dynamics of nanojets has given rise to spectacular experimental studies and theoretical simulations [1]. Another ideal system is represented by gas confined in nanocavities. It is the case of inert gas atoms coalescing as a fluid or a solid to fill nanocavities in metals, with spherical or faceted morphologies depending of the local pressure. In the case of Xe in Al, an interfacial ordering has been demonstrated by high resolution electron microscopy [2]. These small gas-filled cavities therefore behave as high-pressure cells, providing the boundary conditions for the evaluation of the physical properties of encapsulated gases. A most challenging problem is the evaluation of gas density and pressure in such cavities.Among the possible systems, He nanobubbles in metals have attracted the attention of many researchers, because of their high technological interest in the aging of the mechanical properties of materials involved in nuclear reactors [3]. Measurements averaging the information over large populations of bubbles, the size distribution of which being controlled by TEM, have first been performed by NMR [4] and by a combination of optical absorption and electron energy-loss spectroscopy (EELS) [5]. The first of these studies has revealed a solid-fluid transition at 250K for bubble pressures ranging from 6 to 11 GPa (i.e. He atomic densities from about 100 to 200 nm −3 ). The second study comparing UV absorption spectroscopy on a synchrotron and high energy resolution EELS without spatial resolution on He + implanted Al thin foils, have identified the blue shift of the He 1s → 2p transition (with respect to its value of 21.218 eV for the free atom) as a hint for evaluating the local pressure . Theoretically, Lucas et al. [6] have confirmed that this blue shift of the He K-line should be attributed to the short-range Pauli repulsion between the electrons of neighboring He atoms. Consequently, this effect should increas...